Japan has acknowledged that it conducted only a limited investigation before claiming there was no official evidence that its imperial troops coerced Asian women into sexual slavery before and during World War II.

A parliamentary statement signed Tuesday by Prime Minister Shinzo Abe acknowledged a document produced by a postwar international military tribunal containing a Japanese soldier's testimony about abducting Chinese women as military sex slaves.

That evidence was not included in Japan's only investigation of the issue, in 1991-1993. Tuesday's parliamentary statement said documents showing forcible sex slavery may still exist.

Abe has acknowledged so-called "comfort women" existed but denied they were coerced into prostitution, citing a lack of official evidence. He stated that view as prime minister in 2007, and reiterated it in February after he regained power.